摘要 :
Abstract Dielectric spectroscopy measures the dynamics of polymer melts over a broad frequency range. Developing a theory for the spectral shape can extend the analysis of dielectric spectra beyond determining relaxation times fro...
展开
Abstract Dielectric spectroscopy measures the dynamics of polymer melts over a broad frequency range. Developing a theory for the spectral shape can extend the analysis of dielectric spectra beyond determining relaxation times from the peak maxima and adds physical meaning to shape parameters determined with empirical fit functions. Toward this goal, we use the experimental results on unentangled poly(isoprene), and unentangled poly(butylene oxide), polymer melts, to test whether the concept of end blocks could be one reason for the Rouse model deviating from experimental data. These end blocks have been suggested by simulations and neutron spin echo spectroscopy and are a consequence of the monomeric friction coefficient depending on the position of the bead in the chain. The concept of an end block is an approximation which partitions the chain in a middle and two end blocks to avoid overparameterization by a continuous position dependent change of the friction parameter. Analysis of dielectric spectra shows that the deviations of the calculated from the experimental normal mode cannot be related to the end block relaxation. However, the results do not contradict an end block hiding below the segmental relaxation peak. It seems that the results are compatible with an end block being the specific part of the sub-Rouse chain interpretation close to the chain ends.
收起
摘要 :
When designing polymeric capacitors, it is important to understand the structure-property relationship between chemical functionalities and dielectric properties to tailor materials for specific applications in terms of dielectric...
展开
When designing polymeric capacitors, it is important to understand the structure-property relationship between chemical functionalities and dielectric properties to tailor materials for specific applications in terms of dielectric constant, dielectric loss, band gap, breakdown strength, etc. Herein, we report a clear structure-property relationship with dielectric constant and dielectric loss in a series of polyurea and polyurethane thin films. We demonstrate that the dielectric constant systematically increases and the dielectric loss decreases as the number of carbons between polarizable functional groups decreases. Our syntheses are guided with data obtained from high-throughput density functional theory calculations. By modeling 382 polymer systems, we have determined that a dielectric constant >4 is achieved with at least one aromatic group and at least one of the following moieties: -NH-, -C(O)-, or -O-.
收起
摘要 :
This work presents the synthesis and characterizaiton of three new poly(itaconate)s containing nitriles functional groups as high dipole moment entities and three different cycloalkyl pendant groups, in order to increase the rigid...
展开
This work presents the synthesis and characterizaiton of three new poly(itaconate)s containing nitriles functional groups as high dipole moment entities and three different cycloalkyl pendant groups, in order to increase the rigidity of the system and therefore, their dipolar glass polymer temperature interval. The structural, thermal and dielectric characterization has been carried out in terms of Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS), respectively. All polymers showed good thermal properties with degradation temperatures above 250 degrees C, presenting higher glass transition temperatures than those of recently reported poly(itaconate)s. Regarding dielectric properties, dielectric constant values between 4.0 and 4.3 (at 25 degrees C and 1 kl lz) and relative low loss tangent values (below 0.01) were obtained. BDS measurements showed in all cases, notorious sub -glass transitions even at temperatures below - 100 degrees C, resulting in a broad temperature interval in which these polymers could work without high dielectric losses. Therefore, these materials seem to be good candidates for dielectric applications such as energy storage, among others.
收起
摘要 :
This work presents the synthesis of new poly(itaconate)s containing one or two nitrile pendant groups through conventional radical polymerization. To the best of our knowledge, this is the first time in which the synthesis of poly...
展开
This work presents the synthesis of new poly(itaconate)s containing one or two nitrile pendant groups through conventional radical polymerization. To the best of our knowledge, this is the first time in which the synthesis of poly(itaconate)s containing nitrile groups is reported in the literature. The effect of nitrile groups on the main properties is analyzed. Polymer structures were confirmed by Fourier transform infrared spectroscopy (FTIR), H-1 and C-13 NMR. Molecular weights were measured by size exclusion chromatography (SEC), while thermal characterization was achieved by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Dielectric properties were measured using broadband dielectric spectroscopy at different temperatures. Polymers with one or two nitrile groups presented dielectric constant values (at 25 degrees C and 1 kHz) of around 7 and 12.5, respectively, with relatively low dielectric losses with values below 0.02. BDS measurements showed notorious sub-glass transitions attributed to the movement of the dipolar groups under the electric field, even below - 100 degrees C, allowing to achieve dielectric constant values above the average for polymers even at extremely low temperatures. Therefore, these materials could be considered as good candidates for energy storage applications.
收起
摘要 :
Dielectric elastomers are a class of electro-active polymers (EAPs) which have been used for smart structures, such as muscle-like actuators. These materials with compliant electrodes are transducers of electrical to mechanical en...
展开
Dielectric elastomers are a class of electro-active polymers (EAPs) which have been used for smart structures, such as muscle-like actuators. These materials with compliant electrodes are transducers of electrical to mechanical energy, with extremely large strain and good efficiency. A thorough understanding of the physics underlying the nature of different electrode materials can help modify actuator response. The objective of this paper is to investigate the effect of 4 different electrodes (graphite powder, carbon filled grease, silver filled grease and electrically conductive silicone rubber) on the performance of dielectric elastomer actuators. The principle of operation, the method of fabrication and test method of planar actuators are discussed. Effects of different driving voltages and different prestrain values on the actuator response have been studied. Electrical conductivity under strain, electrode surface uniformity and mechanical compatibility with substrate, as the most important parameters of the electrodes, has been investigated. The importance of latter case in terms of curing state and thickness of rubber electrode has been studied, as influential factors in actuator response. Electromechanical coupling efficiency was used as a consequential parameter to compare different electrode performances. It is concluded that this parameter is influenced by the nature of electrodes.
收起
摘要 :
Electroactive polyamides containing dense oligoaniline functionalizations (PAs) were synthesized via oxidative coupling polymerization followed by postpolymerization functionalization, and exhibit excellent solubility, good therma...
展开
Electroactive polyamides containing dense oligoaniline functionalizations (PAs) were synthesized via oxidative coupling polymerization followed by postpolymerization functionalization, and exhibit excellent solubility, good thermal stability and reversible electroactivity. Interesting spectroscopic changes that occurred through chemical oxidation have been shown, which demonstrate the potential of PAs as an electrochromic material. As a result, the electrochromic behaviors of PAs were investigated in detail, exhibiting high contrast value, moderate switching time, and satisfactory coloration efficiency. Tunable conductive and dielectric properties have also been accomplished by varying the incorporation of oligoaniline segments. (c) 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3343-3349
收起
摘要 :
Dense and chevronic thin films of parylene C were fabricated using a physicochemical vapor deposition technique and their dielectric functions were measured as functions of frequency (from 0.1 Hz to 0.1 MHz) and temperature (from ...
展开
Dense and chevronic thin films of parylene C were fabricated using a physicochemical vapor deposition technique and their dielectric functions were measured as functions of frequency (from 0.1 Hz to 0.1 MHz) and temperature (from -140℃ to 260 ℃) using an impedance meter. The real part of the dielectric function of the chevronic thin film was considerably higher than that of its dense counterpart. Higher dielectric strength, loss factor and conductivity for the chevronic parylene suggest an amorphous phase which are more present in this semi-crystalline polymer. X-ray diffractions are now envisaged to confirm this assumption.
收起
摘要 :
In this paper, a complete analysis of the complex dielectric constant of a flexible substrate from the silicon-based polymer- Polydimethylsiloxane (PDMS) is performed, and the obtained results are discussed. Two experimental metho...
展开
In this paper, a complete analysis of the complex dielectric constant of a flexible substrate from the silicon-based polymer- Polydimethylsiloxane (PDMS) is performed, and the obtained results are discussed. Two experimental methods are applied in this research. The first Two-resonator method is based on resonance measurements by excitation of two types of TE- and TM-mode cylinder resonators with PDMS disks, ensure an accurate determination of the dielectric constant and dielectric loss tangent in both parallel and perpendicular directions (e.g., epsilon par, epsilon(perp)). The second method is based on the tight coverage of planar microstrip ring resonators with non- metalized PDMS samples gives reliable information for the equivalent dielectric parameters (e.g., epsilon(eq), tan delta epsilon(eq)). The obtained results show that PDMS substrates have relatively weak but measurable uniaxial anisotropy and well-expressed frequency dependencies of the extracted dielectric parameters in the range 1-40 GHz, namely epsilon(par) similar to 2.82-2.7; epsilon(perp similar to) 2.73-2.52 and epsilon(eq) similar to 2.75-2.64, tan delta epsilon(eq) similar to 0.017-0.048. The results are confirmed by several other complementary methods. The considered pair of methods are also applied in the temperature interval -40/+70 degrees C; the measured temperature dependencies on the dielectric parameters turn out to be relatively strong. The possible origin of the measured PDMS uniaxial anisotropy has been discussed; in fact, it appears mainly in the temperature range -30/+40 degrees C.
收起
摘要 :
The present contribution provides a perspective on the degree to which modern computational methods can be harnessed to guide the design of polymeric dielectrics. A variety of methods, including quantum mechanical ab initio method...
展开
The present contribution provides a perspective on the degree to which modern computational methods can be harnessed to guide the design of polymeric dielectrics. A variety of methods, including quantum mechanical ab initio methods, classical force-field based molecular dynamics simulations, and datadriven paradigms, such as quantitative structure-property relationship and machine learning schemes, are discussed. Strategies to explore, search and screen chemical and configurational spaces extensively are also proposed. Some examples of computation-guided synthesis and understanding of real polymer dielectrics are also provided, highlighting the anticipated increasing role of such computational methods in the future design of polymer dielectrics.
收起
摘要 :
This study presents a comparison of the dielectric properties of composite materials consisting of insulating polymers (polyamides 6 and 12) containing polyaniline as a conductive phase. Samples were obtained by in situ polymeriza...
展开
This study presents a comparison of the dielectric properties of composite materials consisting of insulating polymers (polyamides 6 and 12) containing polyaniline as a conductive phase. Samples were obtained by in situ polymerization of the aniline monomer in the presence of the insulating matrices. The results obtained by dielectric relaxation spectroscopy showed that it was possible to increase the permittivity of the samples by increasing the polyaniline content. Polyamide12-based films exhibit high dielectric permittivities above the percolation threshold. Polyaniline also induces relaxation phenomena, clearly visible at low temperature. It was also shown that the dielectric relaxation phenomena are thermally activated. Some relaxations seem to be of the same nature in polyamides 6 and 12 films because they require nearly the same activation energy.
收起
原文获取